As the administrator of your database, you are responsible for its usage. This includes the apps you install as well as the number of users currently in use. Odoo is many things (ERP, CMS, CRM application, e-commerce backend, and so on) and there is an application for every need, but it is not a smartphone. You should apply caution when adding/removing features, especially applications on your database, since this may impact your subscription amount significantly, or switch you from a free account to a paying one on the online platform.